FED-STD-228A
4.3.2 Polyvinyl acetate. A 0.2 gram specimen of the elastomer compound shall be transferred to a test
tube containing 2 ml. of sulfuric acid, specific gravity 1.83, and the mixture warmed gently. If
decomposition occurs polyvinyl acetate compound is indicated.
4.3.3 Natural rubber and styrene polymers.
4.3.3.1 Pyrolysis test. Alphabetic extenders, if present, may present distinction between natural rubber
and styrene polymers by the pyrolysis method. These materials shall be removed from the rubber
compound by extraction with alcohol. A specimen of about 1 gram shall be transferred to a Soxhlet-type
apparatus containing 50 ml. of alcohol. The specimen shall be extracted for about 4 hours, at such a rate
that about 3 minutes are required to empty and fill the extraction cup, then removed from the cup and
dried for 1 hour at 70° ± 1°C (158° ± 2°F). The dried specimen shall be subjected to the pyrolysis test
described in 4.1 and the material classified by reference to table I.
4.3.3.2 Color test for styrene polymers. The presence of styrene polymers may be further confirmed by
this test. The dried specimen shall be placed in a small flask, 20 ml. of nitric acid, specific gravity 1.43,
added and then refluxed for 1 hour. The refluxed mixture shall be diluted by pouring into 100 ml. of water,
then extracted with 50-, 25- and 25-ml. portions of ether. The ether extracts shall be combined, washed
twice with 15 ml. of water and the washings rejected. The ether solution shall be extracted with three 15-
ml. portions of 5 percent sodium hydroxide, followed by extraction with 20 ml. of water, and the ether
discarded. The sodium hydroxide extracts and washing shall be combined, then made just acid with
hydrochloric acid, specific gravity 1.19, and 20 ml. added in excess. The solution shall be heated on the
steam bath and nitro benzoic acid reduced with 5 grams of granulated zinc. The solution shall be made
alkaline with 20 percent sodium hydroxide, adding sufficient excess to just dissolve the zinc hydroxide
precipitate that forms. The solution shall be extracted twice with ether and the ether discarded. The
aqueous solution shall be made acid with hydrochloric acid, specific gravity 1.19, cooled to room
temperature, and 2 ml. of 0.5 N sodium nitrate added. The solution shall be poured into an excess of a
solution of B-naphthol in 5 percent sodium hydroxide. A vivid scarlet color indicates the presence of
styrene polymers in the elastomer.
4.3.3 Polyisobutylene polymers. The presence of polyisobutylene polymer may be further confirmed by
the following: A bent delivery tube shall be attached to a test tube No. 1 by means of a rubber stopper.
The delivery tube shall pass through a stopper almost to the bottom of the test tube No. 2 having a side
arm. Test tube No. 2 shall be placed in an ice bath. A second delivery tube shall be attached to the side
arm of test tube No. 2 and extended into an open test tube No. 3 containing 0.5 gram of mercuric acetate
in 10 ml. of methyl alcohol. A 1-gram specimen of the rubber compound that has been extracted 4.3.3.2
shall be placed in the first test tube and heated strongly to decompose and distill off the compound into
the second and third test tubes. The liquid that collects in the second test tube shall be rejected. The
third test tube shall be heated to evaporate the methyl alcohol, avoiding excessive heating near the end
of the evaporation. Twenty-five ml. of petroleum ether (b.p. 50° ± 10°C (122° ± 18°F) shall be added to
the test tube, and the mixture boiled and filtered. The filtrate shall be evaporated to a small volume and
chilled in ice to crystallize the mercury derivative. The crystals shall be dried at 35° ± 5°C (95° ± 9°F.)
and the melting point determined. The derivative is believed to be methoxy-iso-butyl-mercuri-acetate with
a melting point of about 55°C (131°F). The test shall be further confirmed by a mixed melting point
determination with the mercury derivative of known polyisobutylene or isobutylene.
4.3.4 Polysulfide rubbers. The polysulfide rubbers are easily identified by means of odor and high sulfur
content. Additional qualitative tests include the pronounced swelling action of acetone (unlike other
rubbers except unvulcanized nitriles) and the extremely rapid reaction (5 to 35 seconds) at 40°C (104°F)
with a mixture of equal volumes of concentrated nitric and sulfuric acids.
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